From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id A7DE26B003D for ; Tue, 3 Feb 2009 18:44:26 -0500 (EST) Received: by ti-out-0910.google.com with SMTP id j3so1180615tid.8 for ; Tue, 03 Feb 2009 15:44:23 -0800 (PST) Date: Wed, 4 Feb 2009 08:44:08 +0900 From: MinChan Kim Subject: Re: [PATCH v2] fix mlocked page counter mistmatch Message-ID: <20090203234408.GA6212@barrios-desktop> References: <20090203042405.GB16179@barrios-desktop> <2f11576a0902030844l64c25496sa5f2892bbb04e47c@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2f11576a0902030844l64c25496sa5f2892bbb04e47c@mail.gmail.com> Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: Andrew Morton , linux mm , linux kernel , Nick Piggin , Rik van Riel List-ID: On Wed, Feb 04, 2009 at 01:44:52AM +0900, KOSAKI Motohiro wrote: > Hi MinChan, > > I'm confusing now. > Can you teach me? No problem. :) > > > When I tested following program, I found that mlocked counter > > is strange. > > It couldn't free some mlocked pages of test program. > > It is caused that try_to_unmap_file don't check real > > page mapping in vmas. > > What meanining is "real" page mapping? What I mean is that if the page is mapped at the vma, I call it's "real" page mapping. I explain it more detaily below. > > > > That's because goal of address_space for file is to find all processes > > into which the file's specific interval is mapped. > > What I mean is that it's not related page but file's interval. > > hmmm. No. > I ran your reproduce program. > > two vma pointing the same page cause this leaking. I don't think so. > > iow, any library have .text and .data segment. then the tail of .text > and the head of .data vma point the same page. > its page was leaked. > > > > Even if the page isn't really mapping at the vma, it returns > > SWAP_MLOCK since the vma have VM_LOCKED, then calls > > try_to_mlock_page. After all, mlocked counter is increased again. > > > > COWed anon page in a file-backed vma could be a such case. > > This patch resolves it. > > What meaning is "anon page in a file-backed"? > As far as I know, if cow happend on private mapping page, new page is > treated truth anon. > vm_area_struct's annotation can explain about your question. struct vm_area_struct { struct mm_struct * vm_mm; /* The address space we belong to. */ .... .... /* * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma * list, after a COW of one of the file pages. A MAP_SHARED vma * can only be in the i_mmap tree. An anonymous MAP_PRIVATE, stack * or brk vma (with NULL file) can only be in an anon_vma list. */ struct list_head anon_vma_node; /* Serialized by anon_vma->lock */ struct anon_vma *anon_vma; /* Serialized by page_table_lock */ .... .... } Let us call it anon page in a file-backed. In this case, the new page is mapped at the vma. the vma don't include old page any more but i_mmap tree still have the vma. So, the i_mmap tree can have the vma which don't include the page if the one is anon page in a file-backed. This problem is caused by that. Is it enough ? > > So, I don't reach to your conclusion yet. please teach me. -- Kinds Regards MinChan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org